U.S. Pat. No. 4,434,562 discloses an ultraviolet curing apparatus for curing U-V sensitive ink which has been applied to a substrate such as a sheet of paper or paperboard stock by a screen printing apparatus. The ink-bearing sheet is carried on a mesh conveyor through a housing in which is located at least one ultraviolet lamp which directs ultraviolet light to impinge on the ink on the upward side of the traveling sheet. The sheet is held down on the open mesh conveyor belt by means of a suction applied from a suction blower unit located beneath the belt. The suction applied also draws air through light baffles which are pervious to air. The suction forces hold the sheet flat against the mesh conveyor belt and against fluttering of otherwise flapping from the surface of the conveyor belt. The ultraviolet lamp generates considerable heat and a second air unit is used to blow air across both sides of the lamp's reflector shield to keep the temperature of the shield at a reasonable temperature. These UV lamps operate at a high temperature, i.e., 1,200.degree. F. to 1,500.degree. F. and the air cooling of inner and exterior sides of the reflector keeps it from becoming too hot. Also, the cooling air removes any harmful ozone generated during the curing process.
The ultraviolet reaction to cure the ink requires a certain amount of heat for its most effective operation. Therefore, it is not desired to cool the irradiation chamber and the sheet to too low a temperature. With the above-described patented apparatus using a 300 watts per inch ultraviolet lamp, the exit temperature of the sheet is generally in the range of 180.degree. F. to 200.degree. F. If the sheet temperature is allowed to be much higher than 200.degree. F., the paper sheet stock may be adversely effected. Often, the sheets with cured ink are stacked in stacks while still warm. This occasions a build up of residual heat in the stack. If the sheets in the stack become too warm, they become limp, this results in the sheets being more difficult to handle with automated equipment.
The apparatus of U.S. Pat. No. 4,434,562 has been successful because it is small and compact in size and is low in cost while being highly effective in curing the UV ink and its handling of the sheets. It is most desireable that any cooling of the sheets for such an apparatus not be at the expense of making the curing apparatus so large or so expensive as to make it a noncommercially viable product.
The present invention is directed to providing a method and apparatus for ultraviolet curing of the sheets with an apparatus of the general type described above and having means for lowering the temperature of the sheets leaving the apparatus.
Accordingly, a general object of the present invention is to provide an ultraviolet curing apparatus having an open conveyor for carrying sheets beneath an ultraviolet lamp having an air cooled reflector and having an air cooling means for the sheets to lower the temperature of the sheets substantially after they exit the UV chamber.
A further object of the invention is to provide a new and improved system for cooling sheets with high velocity air before the sheets exit an ultraviolet curing apparatus and to holding the sheets down on the conveyor while high velocity turbulent air flows across the tops of the sheets.
These and other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.